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| author |   Mark Brown <broonie@kernel.org> | 2022-02-16 17:32:21 +0000 |
|---|---|---|
| committer |   Will Deacon <will@kernel.org> | 2022-02-25 14:41:05 +0000 |
| commit | 3f9ab2a6986fe2930782408cc2a6c25e3e5cb98f (patch) | |
| tree | 41f0a01d44fcf92000a1cac09479e2a05fb4a55d /Documentation/arm64 | |
| parent | arm64: mte: avoid clearing PSTATE.TCO on entry unless necessary (diff) | |
| download | linux-dev-3f9ab2a6986fe2930782408cc2a6c25e3e5cb98f.tar.xz linux-dev-3f9ab2a6986fe2930782408cc2a6c25e3e5cb98f.zip | |
arm64/mte: Document ABI for asymmetric mode
MTE3 adds a new mode which is synchronous for reads but asynchronous for
writes. Document the userspace ABI for this feature, we call the new
mode ASYMM and add a new prctl flag and mte_tcf_preferred value for it.
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220216173224.2342152-2-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'Documentation/arm64')
| -rw-r--r-- | Documentation/arm64/memory-tagging-extension.rst | 21 |
1 files changed, 15 insertions, 6 deletions
diff --git a/Documentation/arm64/memory-tagging-extension.rst b/Documentation/arm64/memory-tagging-extension.rst index 7b99c8f428eb..42677d48a114 100644 --- a/Documentation/arm64/memory-tagging-extension.rst +++ b/Documentation/arm64/memory-tagging-extension.rst @@ -76,6 +76,9 @@ configurable behaviours: with ``.si_code = SEGV_MTEAERR`` and ``.si_addr = 0`` (the faulting address is unknown). +- *Asymmetric* - Reads are handled as for synchronous mode while writes + are handled as for asynchronous mode. + The user can select the above modes, per thread, using the ``prctl(PR_SET_TAGGED_ADDR_CTRL, flags, 0, 0, 0)`` system call where ``flags`` contains any number of the following values in the ``PR_MTE_TCF_MASK`` @@ -85,6 +88,7 @@ bit-field: (ignored if combined with other options) - ``PR_MTE_TCF_SYNC`` - *Synchronous* tag check fault mode - ``PR_MTE_TCF_ASYNC`` - *Asynchronous* tag check fault mode +- ``PR_MTE_TCF_ASYMM`` - *Asymmetric* tag check fault mode If no modes are specified, tag check faults are ignored. If a single mode is specified, the program will run in that mode. If multiple @@ -139,18 +143,23 @@ tag checking mode as the CPU's preferred tag checking mode. The preferred tag checking mode for each CPU is controlled by ``/sys/devices/system/cpu/cpu<N>/mte_tcf_preferred``, to which a -privileged user may write the value ``async`` or ``sync``. The default -preferred mode for each CPU is ``async``. +privileged user may write the value ``async``, ``sync`` or ``asymm``. The +default preferred mode for each CPU is ``async``. To allow a program to potentially run in the CPU's preferred tag checking mode, the user program may set multiple tag check fault mode bits in the ``flags`` argument to the ``prctl(PR_SET_TAGGED_ADDR_CTRL, flags, 0, 0, 0)`` system call. If the CPU's preferred tag checking -mode is in the task's set of provided tag checking modes (this will -always be the case at present because the kernel only supports two -tag checking modes, but future kernels may support more modes), that +mode is in the task's set of provided tag checking modes, that mode will be selected. Otherwise, one of the modes in the task's mode -set will be selected in a currently unspecified manner. +selected by the kernel using the preference order: + + 1. Asynchronous + 2. Asymmetric + 3. Synchronous + +If asymmetric mode is specified by the program but not supported by +either the system or the kernel then an error will be returned. Initial process state --------------------- |